One of the most important parts of any spacecraft is their attitude control system. This is the part which is responsible for keeping the craft pointed in the right direction something which is of the ultimate importance when you’re trying to do things like fine tuning manoeuvres or trying to monitor a specific part of the sky for an extended period of time. The most common of these kinds of systems are reaction control systems which typically use a hypergolic fuel (ignites on mixure, no external ignition source required) however they’re limited by the amount of fuel you can bring with you. Whilst there are many alternatives reaction wheels are the best in terms of weight, size and precision and they can make for cool systems like these:
Cubli isn’t the first reaction wheel controlled robot I’ve seen but it is most certainly the most elegant and precise. It’s also probably the best demonstration I’ve seen of how reaction wheels work, showing aptly how rotational momentum can be translated into an angular force on the objects that the reaction wheel is coupled to. Whilst most space craft won’t ever use the jumping and walking functions (that’s what station keeping boosters are for) the rest of the demonstrated capabilities are identical to what many modern space craft use.
As for uses for things like this on earth? Well there aren’t as many as there are out in space, mostly thanks to us having other means by which to stabilize and rotate things, but they do make for a cool technological demonstration.
Earth is constantly being bombarded with all sorts of things from space. The sun constantly smashes us with solar winds and radiation, asteroids are constantly making their fiery descents and every so often we’ll have one of our own bits of equipment come back down once its reached the end of its life (or sometimes, sooner). Thankfully our atmosphere does a pretty good job of breaking these things up before they reach the ground and most of the time debris from space lands in an unpopulated area, causing little to no harm. Still there’s evidence littering our planet that tells us that large objects from space make their way down to the surface, often with very deadly consequences.
Probably the most famous piece of evidence to support this, even though people don’t usually know it’s name, is the Chicxulub crater on the Yucatan peninsula. This is the crater that is currently believed to be responsible for the mass extinction event that happened approximately 65 million years ago, the one that wiped out the dinosaurs. The impactor, a fancy name for the asteroid that made that giant crater, was estimated to be about 10KM in diameter. The collision has been estimated to have a total energy output of something like 96 teratons of TNT, 2 million times more powerful that the largest nuclear weapon ever detonated. With that kind of power being unleashed it’s then very plausible that it was responsible for the extinction of many species.
The most recent example we have of something like this, although many orders of magnitude less severe, is the Tunguska event which happened in Russia back in 1908. Whilst not technically an impact from an asteroid (or comet, possibly), it is believed that the Tunguska asteroid exploded about 5~10KM above the surface, it still managed to level an area of over 2,000 square kilometres. That’s still powerful enough to take out a major metropolitan area however, so you’d hope that we’d have some strategies for dealing with potential events like this.
Turns out, we do.
Now many people would say “Why wouldn’t you just nuke the bastard” figuring that our most powerful weapon would be more than enough to vaporize a potential threat before it could materialize. The thing is though whilst nuclear weapons are immensely powerful they derive much of their power from the blast wave that they create upon detonation. In space however there’s nothing for them to create a blast wave with so much of the nuke’s devastating power is lost, leaving just the thermal radiation to do its work. Depending on the type of asteroid¹ it will either make the problem worse or simply do nothing at all.
The better option is something called a Gravity Tug, a specially designed spacecraft launched well in advance of the potential impact event to steer the asteroid off course. In essence they’re a simple idea the spacecraft simply approaches the asteroid and then stays next to it, using ion thrusters to keep a set distance between them. Whilst the gravitational effect of the spacecraft on the asteroid is minuscule over time it adds up to be enough to steer the asteroid away from its crash course with earth. Indeed this exact idea is being proposed to deflect the potential impactor Apophsis who’s got a small chance of hitting earth in 2036. Of course this only works for asteroids we know about but our tracking is good enough now that it’s quite hard for a potential disaster causing asteroid to slip through unnoticed.
When it comes down to it having an asteroid cause significant damage is a distinctly rare event with our first line of defence (our atmosphere) doing a pretty good job of breaking up would be impactors. Still it’s good to know that despite the vanishingly small possibility of such a thing happening we’re still prepared for it, even if it means having to launch something years in advance. Maybe we’ll eventually be able to modify that technology to be able to capture asteroids in our orbit so we could utilize them as bases for further operations in space. I’m not holding my breath for that though, but it’s a nice fantasy to have none the less.
¹There are 3 main types of asteroid. The first is basically solid rock compressed together, so the asteroid is one solid object. The second is a collection of rubble that’s held together by the tenuous gravity between all the small fragments. The last are iron asteroids which are solid lumps of metal, which are the really scary ones.
I can remember for the longest time being completely unaware of the asteroid belt between Mars and Jupiter. After learning about it however I never paid much more thought to it, although I was curious about how there seemed to be a line that separated the smaller, rocky planets from the large gas giants of our solar system (negating Pluto, of course). As my interest in space grew I began to wonder how any spacecraft that had ventured past Mars (there have been 9 of them) hadn’t managed to have a run in with a stray asteroid. As it turns out there’s a few reasons for that, and I find them quite fascinating.
The first is that the average density of the asteroid belt is extremely low with the total mass contained within the entire system being less than 4% of that of our Moon. Our best calculations then put the odds of a satellite coming into (unintended) contact with an asteroid in this region at about a billion to one, or so unlikely that you wouldn’t even consider it a risk. The images of the asteroid belt that many are familiar with make it look far more densely packed than it really is, much like this series of pictures that shows all the artificial satellites of Earth. That’s not to say the amount of junk we’ve sent up around ourselves isn’t an issue, but an accurate scale representation of each satellite wouldn’t look anywhere near as packed as they do.
What fascinates me the most about the asteroid belt however is how the majority of the mass is concentrated within 4 objects, with the two largest of these being 4 Vesta and an object big enough to be classed as a dwarf planet called Ceres. In astronomical terms they’re right in our backyard but even with our most powerful space based telescope we’re still only able to capture relatively blurry representations of them, shrouding these little heavenly bodies in mystery. Ceres especially so, with a series of images showing a massive bright spot moving across its surface of which its nature is still unknown.
So fascinating are these objects that NASA launched a mission to both of them, named Dawn, back in 2007. This particular spacecraft is something of a novelty in of itself as well as it is the first purely exploratory mission to use only ion thrusters for propulsion. It needs these highly efficient engines as it will be the first spacecraft to launch to its target, orbit it for a set amount of time and then set off again to approach yet another target. To do this it is carrying with it over 400kg of propellant enough for it to change its velocity by over 10km/s, a figure well above that of any other spacecraft that has come before it. It may take its time in doing so, but it’s still an incredible achievement none the less.
Dawn is scheduled to arrive at its first target, 4 Vesta, in just over a month and it has already begun sending back pictures and video of this strange mega-asteroid. They’re not much to look at right now but once its closer the imagery will become much clearer, revealing the nature of all the blurry spots we’ve as of yet only been able to speculate about. Dawn will spend a year surveying 4 Vesta before it sets off on its long journey for Ceres, for which it is not expected to reach until February 2015. Its a long wait to get a better look at something that’s so small compared to nearly everything in our solar system, but the prospect still excites me immensely.
Perhaps its the combination of their close proximity yet relative lack of information about these two little bodies that makes them so interesting, they’re just sitting there begging to be investigated. The next year will reveal all sorts of insights into the asteroid belt and its second largest contributer which will in turn tell us something about Ceres itself. We’re still a long, long way away from seeing Ceres in the flesh (or rock, as it were) but any information that Dawn sends back is valuable and I can’t wait to see what it brings us.
Getting off the rock which we’re gravitationally bound to is an expensive endeavor, so much so that doing it has well been out of the reach of anyone but the super-governments of the world for almost half a century. We’re in the middle of a space revolution with private companies popping up everywhere promising to reduce the cost of access to space with many of them delivering on their promises. Still even with so many revolutions happening in the private space industry the cost of doing so is still well out of the reach of the vast majority of people in the world, even though they’ve come down by an order of magnitude in the past decade.
Still there are people working on extremely novel solutions to this problem and they’re starting to show some very promising results. Late last year I wrote about Copenhagen Suborbitals a volunteer team that is working on a single person rocket using only donated funds. Back then they were gearing up to launch their first test rocket called HEAT from their sea launch platform that was propelled by a submarine that one of its creators built. Unfortunately they did not manage to launch as the cryogenic valve for the liquefied oxygen had frozen shut (thanks to the hair dryer they used as a heater draining the batteries on the sub) preventing the rocket from igniting. They were determined to launch it however and just recently they gave it another attempt.
The upgraded rocket, dubbed HEAT-1X, has a few improvements over its previous incarnation. The sea launch platform is now a fully enclosed unit, no longer requiring external propulsion from a submarine to get it into position. HEAT-1X now uses a polyurethane rubber mix instead of the previously used paraffin wax which was found to not vaporize completely which caused a reduction in the resulting amount of thrust. With these improvements in mind they attempted launching again back on the 3rd of June, and the results speak for themselves:
The launch, whilst undoubtedly a success for all involved, wasn’t without its share of problems. HEAT-1X did manage to achieve supersonic speed however it deviated from its direct vertical flight path considerably. Even though they were out in the ocean mission control decided to shut down the engine after 21 seconds of flight. The craft still managed to achieve a height of approximately 2.8KM in that time and covered over 8KM in ground distance. There was successful separation of the booster and craft stages however the parachute on the booster was torn free due to the high drag it experienced. The space craft’s parachutes didn’t unfurl properly either causing it to receive significant damage upon landing. Unfortunately the booster was lost to the Baltic Sea but the capsule was recovered successfully.
Despite those problems the HEAT-1X flight represents a tremendous step forward for the Copenhagen Suborbitals team and shows that they are quite capable of building a craft capable of delivering people into suborbital space. They’re still a long way from putting a person in one of their crafts (3~5 years is their estimate) but this launch validates much of the work they have done to this point. I really can’t wait to see them achieve their vision of getting someone into space on a shoestring budget and should they succeed they will make Denmark the fourth nation ever to launch a man into space (Russia, USA and China were ahead of them, if you were wondering). Considering that it will all be done with volunteer time and donations make the achievement even more incredible and I’m sure they’re inspiring many of their younger Danes to pursue a life in the sciences and engineering.
The current way of accessing space isn’t sustainable if we want to make it as a space fairing species. Whilst the methods we use today are proven and extremely reliable they are amongst the most inefficient ways of lifting payload into orbit around our planet, requiring craft that are orders of magnitude larger than the precious cargo they carry. Unfortunately the alternatives haven’t been too forthcoming, due in part to nuclear technologies being extremely taboo and the others still being highly theoretical. Still even highly theoretical ideas can have a lot of merit especially if they have smaller aspects that can be tested and verified independently, giving the overall theory some legs to stand on.
I’ve talked before about the idea of creating a craft that uses only a single stage to orbit (SSTO), in essence a craft that has only one complete stage and conceivably makes extensive use of traditional aerodynamic principles to do away with a lot of the weight that conventional rockets have. My proposal relied on two tested technologies, the scramjet and aerospike engine, that would form the basis of a craft that would be the Model T equivalent for space travel; in essence opening up space access to anyone who wanted it. In all honesty such a craft seeing reality is a long way off but that doesn’t mean people aren’t investigating the idea of building a SSTO craft using different technologies.
One such company is Reaction Engines, a name that I was only marginally familiar with before. They’ve got a proposal for a SSTO craft called Skylon that uses a very interesting engine design that combines both an air breathing jet engine as well as a traditional rocket motors. The design recently passed its first technical review with flying colours and could see prototypes built within the decade:
They want the next phase of development to include a ground demonstration of its key innovation – its Sabre engine.
This power unit is designed to breathe oxygen from the air in the early phases of flight – just like jet engines – before switching to full rocket mode as the Skylon vehicle climbs out of the atmosphere.
It is the spaceplane’s “single-stage-to-orbit” operation and its re-usability that makes Skylon such an enticing prospect and one that could substantially reduce the cost of space activity, say its proponents.
The engine they’re proposing, called Sabre, has an extremely interesting design. At lower speeds it functions much like a normal jet engine however as speeds approach Mach 5, the point at which my hand waving design would switch to a scramjet, it continues to operate in much the same fashion. They do however employ a very exotic cooling system so that the engine doesn’t melt in the 1000+ degree heat that would be blasting the components and once Skylon is out of the atmosphere it switches to a normal rocket engine to finish off the job.
The issues I see, that face nearly all SSTO designs, is the rule of 6 for getting to orbit. The rule simply states that at Mach 6 at 60,000 feet you have approximately 6% of the total energy required to make it successfully to orbit. Skylon’s engines operate in the jet mode all the way up to Mach 5 to an altitude of 85,000 feet which is no small feet in itself, but it’s still a far cry from the total energy required. It is true though that the first stages of any rocket are the most inefficient and eliminating them by using the atmosphere for both oxidiser and thrust could prove to be a real boon for delivering payloads into orbit. Still whether this will be practical with Skylon and the Sabre engine remains to be seen but there are tests scheduled for the not too distant future.
Walking through unknown territory like this is always fraught with unknowns so it’s no wonder that the team at Reaction Engines has been met with such skepticism over their idea. Personally I’m still on the fence as their technology stack is still mostly unproven but I applaud their vision for wanting to build the first SSTO craft. I’d love to see the Skylon making trips to the International Space Station, effectively replacing the shuttle and extending the ISS’ lifetime but until we see some more proof that their concept works I’m going to be skeptical, but it won’t take much to make into a believer
6 months ago I wrote about SpaceX’s historic flight of their Falcon 9 rocket and how much it meant to us space romantics. Their tentative schedule had me all aflutter with the possibility of seeing not one, but two more flights of their flagship rocket within this year. It was looking entirely possible too as just on a month later they were already building the next rocket and there was even a hint that I might get to see it take off on my trip through America. Whilst I may not have gotten to see the launch for myself SpaceX is not one to disappoint with them launching their second Falcon 9 rocket earlier this morning carrying a fully fledged version of their crew and cargo capsule, the Dragon.
The launch itself didn’t go by without a hitch though with some bad telemetry data causing the initial launch to be scrubbed and rescheduled for about an hour later. However once they were past that minor hurdle they were able to continue with launch preparations and launch without incident. This is testament to their ability to rapidly troubleshoot and resolve problems that would likely cost anyone else at least a day to recover from. Elon Musk is definitely onto something when he thought about running a launcher company as a startup, rather than a traditional organisation.
The mission profile was a relatively simple one although it represents a giant leap forward in capability for SpaceX. The previous launch of the Falcon 9 carried with it a Dragon Spacecraft Qualification Unit, basically just a shell of a full Dragon capsule designed to be little more than a weight on top of the Falcon 9 rocket. That capsule lacked the ability to separate from the second stage of the Falcon 9 it was attached to and was also designed to burn up on re-entry. The payload for this mission however was a fully functional Dragon capsule with the full suite of avionics, support systems and the ability to return to earth from orbit. It was also carrying a small fleet of government owned CubeSats that were launched shortly after they achieved orbit. Approximately 3 hours after the Falcon 9′s launch the Dragon capsule returned safely to earth, splashing down in the Pacific Ocean.
I, along with every other space nut out there, are incredibly excited about what this means for the future of space. Not only has SpaceX managed to successfully launch a brand new rocket twice in 6 months they’ve done so with an almost flawless record. The pace at which they’re progressing is really quite astonishing considering how small they are compared to those who’ve achieved the same goals previously. The team that Elon Musk has assembled really deserves all the credit that they get and I now I wait with baited breath at their next launch as that will be the first private spacecraft ever to visit the International Space Station.
It’s really quite exciting to see progress like this in an area that was once considered only accessible by the world’s superpower governments. Whilst we’re still a long, long way from such technology becoming an everyday part of our lives like commercial air travel has the progress that SpaceX has made shows that the current cost to orbit can and will come down over time. This also gives NASA the opportunity to stop focusing on the more rudimentary aspects of flight that SpaceX is now capable of handling, leaving them to return to what they were once known best for: pushing the envelope of what the human race is capable of in space. So whilst we won’t be seeing another Falcon 9 launch this year as I had hoped all those months ago this perfect flight of the first fully functional Dragon capsule signals that the future of space travel for us humans is not just bright, it’s positively blinding.